The present invention is in the field of mechanisms for tracking moving webs. More specifically this invention relates to the tracking method of the film on the film handling system, and a means for adjusting the film tracking, in electrophotographic printers and copiers.
In high speed electrostatographic reproduction apparatus, it is a common practice to employ an elongated photoconductive belt or web adapted to record transferable images while the web is moving in a path in operative relation with various process stations. Typically the web is supported by, and driven about, at least one roller. With a roller support, there is a tendency for the moving web to shift laterally, or cross-track, with respect to such a roller. This tendency can be due to manufacturing tolerances, such as the inability to manufacture perfectly cylindrical rollers, or to exactly mount the rollers in a web supporting system. Various apparatus for correcting such lateral shifting of roller-supported webs are known, such as crowned rollers, flanged rollers, servo-actuated steering rollers, or self-actuating steering rollers. Crowned rollers generally are not suitable for use with a web in an electrostatographic reproduction apparatus, because they force the web toward the apex of such rollers, cause distortion of the web, and produce local stresses in the web at the crown which can damage the web. Flanged rollers generally are also not suitable because they produce a concentrated loading at the edges of the web, resulting in edge buckling, seam splitting, or excessive edge wear.
Electrostatographic reproduction apparatus therefore typically utilize servo-actuated or self-actuated steering rollers. While such steering rollers generally correct in a gross manner the cross-track shifting of the web, they tend to produce significant lateral movement of the web at an uneven rate as it is re-aligned. This can adversely effect the resulting image quality.
Another method for web tracking is disclosed in U.S. Pat. No. 4,901,903 by Blanding, which describes a steering roller mounted on a pivoted yoke, wherein the roller has an edge guide, and an edge guide adjustment mechanism. In this method, a light tension spring applies a force to the yoke to rotate the roller about a caster axis to impede aberrant lateral movement, and provide corrective action should it occur. This method, though useful, takes a fair amount of very limited space. It is also difficult to make fine adjustments to the tracking using the apparatus disclosed in Blanding.
A method and apparatus for web tracking, and web tracking adjustment is desired which is simple, cost effective, can more effectively use the limited space, and which can make fine adjustments.